The objective of the project is to discover processes that determine neuron morphology and synaptic connectivity in a network of neurons which are individually identifiable. Specifically, three problems are being investigated, in sensorimotor systems of the crayfish abdomen and the earthworm. 1) If homologous neurons in different segmental ganglia are interconnected differently, what processes underlie development of these differences? 2) What is the time course of development of identifiable neurons which are programmed to form synaptic connections? 3) Does connectivity of a given pair of identifiable neurons vary among organisms? If so, how strictly does the developmental program regulate the formation of synapses between the neurons?